Disease & heat resistance

Breeding for resistance to bovine tuberculosis in Irish cattle

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Abstract

Bovine tuberculosis (bTB) is an infectious disease of cattle caused primarily by Mycobacterium bovis. Despite focused national bTB eradication efforts, bTB remains prominent in Ireland. Prevalence of bTB has increased from 4.38% in 2020 to 6.08% in 2025, notwithstanding total government expenditure of €79.4m from Q1 to Q3 in 2025. In 2019, the Irish Cattle Breeding Federation (ICBF) introduced estimated breeding values (EBVs) for bTB resistance as a stand-alone trait, and in 2022 this trait was integrated into national economic breeding models for dairy and beef production systems. This enabled genetic selection for bTB resistance in Irish cattle and demonstrated how genetic selection can guide farmers in reducing bTB in their herds. Within the ICBF bTB resistance genetic evaluation, whole-herd skin test results and post-mortem TB results (from abattoirs) from animals in infected herds, along with their herd-mates, are included to allow comparisons among cattle with similar exposure and management conditions. bTB exposure is represented within the evaluation using a binary infection phenotype (0 = non-reactor, 1 = reactor). Each animal's breeding value for resistance to bTB is expressed as the predicted prevalence percentage of bTB in that animal's progeny, with lower values indicating greater genetic resistance in subsequent progeny. The heritability of bTB infection prevalence was estimated at 0.12 which indicates a moderate genetic contribution to bTB resistance. Analysis conducted by the ICBF found that high genetic merit sires with ≥50 progeny across ≥10 bTB-infected herds had substantial variation in bTB prevalence within the progeny from these sires. Findings demonstrated that a proportion of bulls sired no bTB infected progeny despite exposure within high-risk herds, whereas other sires produced up to 40% bTB positive progeny in high-risk herds. Further analysis of bTB infected animals showed the number of bTB reactors was 26% higher in cattle with poor EBVs versus those with more favourable EBVs for bTB resistance. Therefore, farmers that integrate low bTB EBVs promotes bTB genetic resistance. Among AI bulls born in the last 10 years, EBVs for bTB resistance ranged from 4.79% to 12.49% across the 1st to the 99th percentiles with a median of 8.41%, indicating that considerable genetic variation exists. To simplify breeding decisions, the ICBF have set up a traffic-light system which classifies animals as green, orange, or red corresponding to high (favourable), medium, and low (unfavourable) bTB EBVs. When selecting animals for breeding, the lower the bTB EBVs that can be achieved without impacting production traits, the better. Incorporating a bTB resistance trait into overall breeding objectives in conjunction with a decision support tool for farmer understanding aids breeding strategies towards bTB resistance in Ireland.

Keywords: 2026

How to Cite:

Lanigan, S. & Ring, S., (2026) “Breeding for resistance to bovine tuberculosis in Irish cattle”, World Congress on Genetics Applied to Livestock Production Digital Archive 2026(1): 2285542. doi: https://doi.org/10.31274/wcgalp.23735

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